Stabilization of organic substances



Patented Nov. 28, 1944 STABILIZATION OF ORGANIC SUBSTANCES Charles J. ledersen, Penns Grove, N. 1., asslgnor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 1, 1942, Serial No. 467,555

23 Claims.

This invention relates to the stabilization of organic substances and particularly to the stabilization of such substances which are subject to deterioration caused by the action of molecular oxygen and catalyzed by metals and their compounds.

Many organic products, such as fats, drying oils, rubber, petroleum products, photographic developers and synthetic unsaturated compounds, are readily attacked by oxygen and the resulting deterioration imparts undesirable qualities to them and eventually destroys their usefulness.

Signal success has been achieved in recent years, in the preservation of many organic substances, by the discovery and use of compounds generically called oxidation inhibitors or "antioxidants." These agents, mostly oxidizable organic compounds, retard the auto-catalytic process. Since antioxidants are themselves oxidized in the course of time, as a result of auto-oxidation, the beneficial eilect obtained by their use is not permanent, and they protect the organic substances only so long as they are not rendered inactive. They are, moreover, very specific in action, each group of auto-oxidizable substances rethe oxidation of aromatic hydroxy and amino antioxidants used to stabilize these oxidizable substances. Hence, these metal catalysts and the antioxidants are antagonistic in action, and the normal inhibiting effect of the latter is greatly reduced in the presence of the former.

Metal compounds occur naturally in many organic products, but often in such slight traces as to cause very little harm. Their concentrations, however, are frequently raised during the course of handling and utilizing the products; vessels and conduits made of metals containing copper are used for storage and transportation, or ingredients contaminated with metal compounds might be added.

The harm done by these extraneous catalysts may be prevented by at least three methods: (1) their removal by purification, but often this is practically impossible of accomplishment and usually too costly to be economically feasible, (2) the additionof a suflicient amount of an antioxidant so that its preserving eflect is equal to or greater than the pro-oxidant efiects of the metal catalysts present, but the effectiveness of the antioxidant is so greatly diminished by the metal catalysts that the advantage gained under this circumstance is seldom worth the cost of the increased quantity of antioxidant required for adequate stabilization, and (3) the suppression of the catalytic activity of the metal compounds by chemical means without physically removing them from the system.

It is an object of the present invention to retard the deterioration of organic substances caused by the action of molecular oxygen and promoted by the presence of certain metal catalysts and their catalytically active compounds. Another object is to render anti-oxidants, which are relatively ineffective in the presence of metal catalysts and their catalytically active compounds, eflfective to inhibit the oxidation of oxidizable organic substances even in the presence of metal catalysts and their catalytically active compounds. A further object is to provide a new class of metal deactivators which are efiective to render metal catalysts inactive to catalyze the oxidation of oxidizable organic substances containing or in contact with such metal catalysts. A more particular object is to inhibit the deterioration of petroleum hydrocarbons in the presence of metal catalysts and their catalytically activ compounds. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with my invention which comprises added to organic substances, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said organic substances, a metal deactivator in a small proportion sufficient to deactivate such catalysts, such metal deactivator being a heterocyclic carboxylic acid compound in which the heterocyclic ring consists of 1 nitrogen atom and a plurality of carbon atoms. The organic substance also may and generally will contain an antioxidant which is normally effective to retard oxidation of the organic substance in the absence of the metal catalyst. I have found that such metal deactivators are capable of effectively suppressing the catalytic activity of manganese, copper and their catalytically active compounds and hence will render such catalysts ineffective to catalyze the oxidation of the organic substance, including any anti-oxidant which may be present.

The organic substances, which may be treated in accordance with my invention, include animal and vegetable fats and oils, edible oils, fruit and vegetable juices, textile fibres, photographic developers, antioxidants, synthetic unsaturated compounds, petroleum hydrocarbons, rubber and the like. My metal deactivators are particularly desirable in liquid petroleum hydrocarbons and especially in gum-forming hydrocarbon distillates, such as, for example, cracked gasoline. Generally, in practice, the organic substance, particularly the petroleum hydrocarbons, will also contain an antioxidant which is normally effective to materially retard the deterioration or oxidation of the organic substance in the absence of the catalytically active metals, but which is less effective in the presence of such metals.

The metal deactivators of my invention are the heterocyclic carboxylic acids, in which one heterocyclic ring atom is nitrogen and the remainder are carbon atoms, and the salts of such acids. Generally, the free acids will be preferred. However, their salts, such as the salts of the alkali metals, ammonium and organic substituted ammonium, are also effective and, because of their solubility characteristics, will be more desirable in certain cases. Accordingly, by the term heterocyclic carboxylic acid compound," I mean to include both the free acids and the salts thereof. Preferably, the carbon atom of the carboxyl group, --CO, will be bonded to a carbon atom of the heterocyclic ring which carbon atom is adjacent to the nitrogen atom of such ring, Also, preferably, the heterocyclic ring will be a G-membered ring consisting of 1 nitrogen atom and carbon atoms, as in pyridine, quinoline, piperidine and 1,2,3,4 tetrahydro-quinoline. I further prefer that the heterocyclic carboxylic acid be one which, except for the ring nitrogen and the carboxyl oxygen atoms, consists of carbon and hydrogen. I especiall prefer the monocyclic heterocyclic carboxylic acids, and particularly the monocarboxylic acids, as these appear to be the most effective. By a monocyclic heterocyclic carboxylic acid, I mean one which contains only a single ring, that ring being the heterocyclic ring. By a moncarboxylic acid, I mean one which contains only one carboxyl group.

Definite operative concentrations of the metal deactivator in the organic substance cannot be specified for each case as the quantity required 'is dependent upon the amount of metal catalyst present in the organic substance. The metal deactivator should be present in the proportion of approximately 5 to 30 times the amount of the metal catalyst present, on the basis of the metallic element, in order to obtain complete deactivation of the metal catalyst. Higher proportions of metal deactivator may be employed, particularly when a reservoir of metal is present in the form of metal in bulk in contact with the organic substance. Generally, from about 0.0001% to about 1.0%, based on the weight of the organic substance, will be sufiicient for most purposes, particularly when the organic substance is a liquid petroleum hydrocarbon, such as a gum-forming hydrocarbon distillate of the character ofcracked gasoline.

The catalytically active'metal and its compounds may be dissolved in the organic substance or suspended therein or may be in the form of metal in bulk in intimate contact with the organic substance. It will be understood that, when I refer to an organic substance containing a catalyst, I mean to include those cases wherein the metal in bulk form is in contact with the organic substance, as well as those cases wherein the catalytically active metal is dissolved or suspended in the organic substance.

The deactivators may be added to the oxidizable organic substances to be protected in any form and manner. They may be in solid or liquid form, mixed with other additional agents or dissolved in a solvent. 7 They may be dissolved in the organic substance or dispersed therein in any suitable manner. They may be added to the finished organic substance or to" the organic substance at any suitable stage in its manufacture.

In order to avoid confusion arising from a superabundance of data, cracked gasoline has been selected as an example of an auto-oxidizable organic substance for the purposes of illustration. The samples of gasoline, used in the following tests, were either cracked gasolines or blends of cracked and straight-run gasolines, completely refined, but otherwise untreated with chemical agents, such as dyes, anti-knocks and antioxidants. Since gasoline is a mixture of variable composition,- identical results are not obtained with different samples. The magnitude of the effects is great enough, however, to render this difference relatively insignificant.

The metals, present as catalysts, were employed as their oleates. The concentrations of the antioxidants and the metal deactivators are given in weight percent in gasoline. The concentrations of the metals are given in parts per million by weight of the metal rather than by weight'of the metal oleate.

The term stabilized gasoline is employedto denote gasoline to which has been added an antioxidant in sufficient quantity to significantly increase its induction period in the absence of added metal catalysts.

The accelerated method, used for determining the induction periods given below, was the one described in J. I. E. C. 25, 397 (1933). It consists in heating cc. of gasoline at 100 C. in a 1 liter pyrex flask containing pure oxygen. The internal pressure is observed every 10 minutes by means of a manometer attached to the system.

The elapsed time, from the start of the test until the gasoline begins to adsorb oxygen at the rate of 10 cc. per 10 minutes or higher, as shown by the fall in internal pressure, is taken as the induction period. It has been found that the induction period, obtained by this methed, although greatly shortened, is a fairly accurate measure of the relative stability of gasoline under normal storage conditions.

The experimental results, obtained with representative compounds belonging to this class of deactivators, are shown in the following tables.

Table I Induction period of control minutes.

This gasoline, containing 0.0025% p-(n-butylamino) phenol and having an induction period of 390 minutes in the absence of added metals, was used for these tests.

per and manganese are counteracted by the two deactivators.

The deactivators are also effective in decreasing the copper dish gum, even when used alone, that is, in the absence of an antioxidant. This is shown by the data in Table II.

Compounds, in which the carboxyl group is attached to the ring carbon atom not adjacent to the ring nitrogen atom, are also deactivators, but they are less effective than those in which the carboxyl group is adjacent to the nitrogen. An example of such a compound is pyridine-fi-carboxylic acid known as nicotinic acid.

It will be understood that the experiments and tests, hereinbefore given, have been given for 11- lustrative purposes only. Many variations and modifications can be made in my invention without departing from the spirit or scope thereof. The metal deactivators of my invention can be employed in other organic substances, the metals may be present in other forms and other compounds, within the broad scope of my invention, may be substituted for the compounds specifically referred to hereinbefore. While I have disclosedthe use of single metal deactivators, it will be apparent that mixtures of two or more metal deactivators of my invention may be employed if desired.

Besides many others, the following compounds are Within the scope of my invention.

2-methylpyridine-6carboxylic acid i-methylpyridine-6-carboxylic acid. Pyridine-2,6-dicarboxylic acid Pyridine-2,3-dicarboxylic acid Pyridine-2,4-dicarboxylic acid 2,4-dimethylpiperidine-G-carboxylic acid 2-methylpiperidine-6-carboxylic acid Quinoline-2-carboxylic acid 4-methylquinoline-2-carboxylic acid. Quinoline-2,3-dicarboxylic acid Quinoline-ZA-dicarboxylic acid 4-methyl (1,2,3,4 tetrahydroquinoline) 2 carboxylic acid Quinoline-8-carb0xy1ic acid 1,2,3,4-tetrahydroquinoline-B-carboxylic acid.

It will be apparent that, by my invention, I am able to effect the stabilization of organic substances susceptible to the harmful action of molecular oxygen catalyzed by manganese, copper and their catalytically active compounds. This stabilization may be accomplished, in accordance with my invention, by the addition of metal deactivators either alone or in combination with an amount of an antioxidant suificient to stabilize the substance in the absence of metal catalysts. It is often technically and economically unfeasible to counteract the catalytic efiects of such metals by means of an antioxidant alone. I believe that the metal deactivators of my invention function by forming very stable complexes with the metals, which complexes are catalytically inactive. It appears that the metal deactivators of my invention, in general, are not antioxidants. However, my invention is not to be limited by any theory as to the manner in which the metal deactivators function to produce the results.

I claim:

1. A composition comprising'an organic sub stance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting or manganese, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a heterocyclic carboxylic acid in which the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring adjacent to the nitrogen atom of such ring.

2. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and theircompounds, normally effective to catalyze oxidation of said organic substance, and having incorporated therein a metal de' activator in a small proportion sufllcient to deactivate said catalyst, said metal deactivator being a heterocyclic carboxylic acid inwhich the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring adjacent to the nitrogen atom of such ring, and which acid, except for the ring nitrogen and the carboxyl oxygen atoms, consists of carbon and hydrogen.

- 3. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a monocyclic heterocyclic carboxylic acid in which the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms, the carbon atom of a carboxyl group being bonded to a ring carbon atom adjacent to the ring nitrogen atom.

4. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally efiective to catalyze oxidation of said organic substance, and having incorporated therein a metal deacti vator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a monocyclic heterocyclic monocarboxylic acid in which the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms, the carbon atom of the carboxyl group being bonded to a ring carbon atom adjacent to the ring nitrogen atom, and which acid, except for the ring nitrogen and carboxyl oxygen atoms, consists of carbon and hydrogen.

5. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally efiective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion sufllcient to deactivate said catalyst, said metal deactivator being picolinic acid.

6. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds. normally effective to catalyze oxidation of said petroleum hydrocar- Y deactivate said catalyst, said metal deactivator being a heterocyclic carboxylic acid in which the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms. the carbon atom or a carboxyl group being bonded to a carbon atom or the heterocyclic ring adjacent to the nitrogen atom 01' such ring, and which acid, except for the ring nitrogen and the carboxyl oxygen atoms, consists of carbon and hydrogen.

'7. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said petroleum hydrocarbons, and having incorporated therein a metal deactivator in a small proportion sufllcient to deactivate said catalyst, said metal deactivator being a monocyclic heterocyclic monocarboxylic acid in which the heterocyclic ring consists oi 1 nitrogen atom and 5 carbon atoms, the carbon atom of the carboxyl group being bonded to a ring carbon atom adjacent to the ring nitrogen atom, and which acid, except for the ring'nitrogen and carboxyl oxygen atoms, consist of carbon and hydrogen.

8. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst oi the group consisting of manganese, copper and their compounds, normally eflective to catalyze oxidation of said petroleum hydrocarbons, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being picolinic acid. 1

9. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and a small proportion of an antioxidant, normally eilective to materially retard such deterioration in the absence 01 said catalyst but which is less eflective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a heterocyclic carboxylic acid in which the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring adjacent to the nitrogen atom of such ring, and which acid, except for the ring nitrogen and the carboxyl oxygen atoms, consists of carbon and hydrogen.

10. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said-organic substance, and a small proportion of an antioxidant, normally eiiective to materially retard such deterioration in the absence of said catalyst but which is less eflective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion suilicient to deactivate said catalyst, said metal deactivator being a monocyclic heterocyclic monocarboxylic acid in which the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms, the carbon atom or the carboxyl group being bonded to a ring carbon atom adjacent to the ring nitrogen atom, and which acid, except for the ring nitrogen and carboxyl oxygen atoms, consists oi carbon and hydrogen.

and having incorporated therein a metal deactivator in a small proportion sumcient to deactivate said catalyst, said metal deactivator bein a member of the group consisting of heterocyclic carboxylic acids inwhich the heterocyclic ring consists of l nitrogen atom and a plurality of carbon atoms, the carbon atom oi a carboxyl group being bonded to a carbon atom of the heterocyclic ring, and the alkali metal, ammonium and organic substituted ammonium salts of such acids.

12. A composition comprising an organic substance, normall subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation or said organic substance, and having incorporated therein a metal deactivator in a small proportion suilicient to deactivate said catalyst, said metal deactivator being a heterocyclic carboxylic acid in which the het erocyclic ring consists 01 1 nitrogen atom and a plurality of carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring adjacent to the nitrogen atom of such ring.

13. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally eilfective to catalyze oxidation of said organic substance,

and having incorporated thereina metal deactivator in a small proportion sufllcient to deactivate said catalyst, said metal deactivator being a heterocyclic carboxylic acid in which the heterocyclic ring consists of l nitrogen atom and a plurality of carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring.

14. A composition comprising an organic substance. normally subject to deterioration caused by the action or molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally efiective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion sufllcient to deactivate said catalyst, said metal deactivator being a heterocyclic carboxylic acid in which the heterocyclic ring consists of 1 nitrogen atom and 5 carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring.

15. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally eflective to catalyze oxidation 01' said petroleum hydrocarbons, and having incorporated therein a metal deactivator in a small proportion suilicient to deactivate said catalyst, said metal deactivator being a member of the group consisting of heterocyclic carboxylic acids in which the beterocyclic ring consists of 1 nitrogen atom and a plurality of carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring, and the alkali metal, ammonium and organic substituted ammonium salts of such acids.

16. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said organic substance, and a small proportion of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less efiective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being a member of the group consisting of heterocyclic carboxylic acids in which the heterocyclic ring consists of 1 nitrogen atom and a plurality of carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring, and the alkali metal, ammonium and organic substituted ammonium salts of such acids.

17. A composition comprising petroleum hydrocarbons, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally efiective to catalyze oxidation of said petroleum hydrocarbons, and a small proportion of an antioxidant, normally efiective to materially retard such deterioration in the absence of said catalyst but which is less eflective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufiicient to deactivate said catalyst, said metal deactivator being a member of the group consisting of hetero cyclic carboxylic acids in which the heterocyclic ring conists of 1 nitrogen atom and a plurality of carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring, and the alkali metal, ammonium and organic substituted ammonium salts of such acids.

18. A composition comprising gasoline, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said gasoline, and a small proportion of an antioxidant, normally efiective to materially retard such deterioration in the absence of said catalyst but which is less eflective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion suflicient to deactivate said catalyst, said metal deactivator being a member of the group consisting of heterocyclic carboxylic acids in which the 'heterocyclic ring consists of 1 nitrogen atom and a plurality of carbon atoms, the carbon atom of a carboxyl group being bonded to a carbon atom of the heterocyclic ring, and the alkali metal, ammonium and organic substituted ammonium salts of such acids.

19. A composition comprising gasoline, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally eflect'ive to catalyze oxidation of said gasoline, and a small proportion of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less efiective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufiicient to deactivate said catalyst, said metal deactivator being picolinic acid.

20. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of thegroup consisting of manganese, copper and their compounds, normally efiectlve to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion sumcient to deactivate said catalyst, said metal deactiva or being 2-methylpyridine-6-carboxylic acid. 21. A composition comprising gasoline, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally efiective to catalyze oxidation of saidgasoline, and a small proportion of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less effective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being 2-methylpyridine-6-carboxylic acid.

22. A composition comprising an organic substance, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally efiective to catalyze oxidation of said organic substance, and having incorporated therein a metal deactivator in a small proportion sufficient to deactivate said catalyst, said metal deactivator being pyridine-2,4-dicarboxylic acid.

23. A composition comprising gasoline, normally subject to deterioration caused by the action of molecular oxygen, containing a catalyst of the group consisting of manganese, copper and their compounds, normally effective to catalyze oxidation of said gasoline, and a small proportion of an antioxidant, normally effective to materially retard such deterioration in the absence of said catalyst but which is less effective in the presence of said catalyst, and having incorporated therein a metal deactivator in a small proportion sufiicient to deactivate said catalyst, said metal deactivator being pyridine-2,4-dicarboxylic acid.

CHARLES J. PEDERSEN. 

